JP2003-32808A, published by the Japan Patent Office, discloses a mechanism (to be referred to as E-iVT hereafter) for performing continuous speed variation by connecting an engine, first and second motor generators, an output gear which outputs a driving force to a drive wheel, and a brake to five rotational elements of a two freedom-degree differential mechanism.
In a travel mode in which the vehicle travels with the brake disengaged, continuous speed variation can be realized by controlling the rotation speeds of the engine and the first and second motor generators, and in a travel mode in which the vehicle travels with the brake engaged, a fixed speed ratio, in which the rotation speed of the engine and the rotation speed of the output gear are fixed, is realized.
A clutch is interposed between the engine and differential mechanism, and by switching the engagement state of the clutch, it is possible to switch between a travel mode in which the vehicle travels on the motive power of the first and second motors alone, regardless of the motive power of the engine, and a travel mode in which the vehicle can travel using the motive power of the engine in addition to the motive power of the first and second motors.